| Connection cable |
| When one speaks about headphones, the emphasis is on such things as sound quality and frequency response. There is rarely any mention of the connection cable. Most Sennheiser headphones are fitted with an OFC (oxygen-free copper) cable. This ensures linear and low-loss transmission in the broad frequency spectrum of the headphones. Many Sennheiser headphones also have detachable cables, which make it very easy to replace them. |
| Contact pressure |
| The wearing comfort of a set of headphones is determined not only by its weight but also by the force with which the earpieces are pressed onto the ears. This force is given in newtons (N), whereby 1 N corresponds to the compressive force which a mass of about 100 g exerts on a solid surface. The DIN Standard 45500 Part 10 limits the maximum permissible contact force to 5 N. Values of between 1.3 and 4 N are common, although lower values apply for open headphones. Higher values can be found in the case of closed headphones. Here, a higher contact pressure is required in order to achieve sufficient sealing, which is important for the reproduction of low frequencies. |
| Ear coupling |
| A distinction is made between headphones which are worn on the external ear (supra-aural) and those which surround the ear (circumaural). Open headphones have foam ear pads that rest on the ears or ring pads that surround the ears. Closed headphones, on the other hand, nearly always have circumaural ear pads. |
| Frequency response |
| The frequency response of a microphone is given within the limits defined by the manufacturer. In studio condenser microphones it is generally within the range of between 20 Hz and 20 kHz. |
| Load rating |
| The load rating is the amount of electric power which - according to the manufacturer´s specifications - can be continuously supplied to a set of headphones over a period of time without causing damage. According to DIN 45500 Part 10, the load rating must be at least 100 mW. Testing is carried out using a special noise signal which is supplied to the headphones over a period of 100 hours. |
| Min. terminating impedance |
| Impedance at which the connected unit meets the specified technical data. If the unit is connected to a lower impedance, it will usually have a lower output voltage or a greater distortion. |
| Nominal impedance |
| See impedance. |
| Pick-up pattern |
| Also known as polar pattern, directivity. According to their acoustic design, microphones differ in their sensitivity towards sound from different directions. Pressure microphones have a sensitivity that is largely independent of direction (omni-directional pick-up pattern). Pressure gradient microphones have the pick-up patterns wide cardioid, cardioid, super-cardioid or figure-of-eight. Interference microphones can be used to achieve a further concentration of the pick-up pattern (lobar pick-up pattern). As a special case, dummy head microphones achieve the pick-up pattern of the human ear/head (dummy head stereo). |
| Sensitivity in free field, no load (1kHz) |
| Voltage measured at the unloaded output of a microphone which is exposed to a sound pressure of 1 Pa and a frequency of 1 kHz in an anechoic chamber. |
| Sound pressure level (SPL) |
| Due to the impractical numerical values, the sound pressure is usually given as the logarithmic value of the sound pressure level according to the equation: dB SPL = 20 x log (po / 0.00002 Pa). The abbreviation SPL (sound pressure level) is added in order to make a clear distinction from other uses of dB. The reference sound pressure, which is at the same time the threshold of hearing, is then 0 dB SPL. The threshold of pain is 140 dB SPL. A difference in the sound pressure level of 1 dB is just about perceptible, while a doubling of the sound pressure corresponds to 6 dB and a doubling of the volume corresponds to a rise of 10 dB.
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| Total harmonic distortion (THD) |
| Total harmonic distortion is a measure of non-linear harmonic distortion and is given in %. Non-linear harmonic distortions are signals which were not present in the original before the signal was converted by the headphones. These unwanted signals are caused by the diaphragm, whose movements do not precisely move in time with the electric signals that cause it to move. Unfortunately, this is a feature of all electroacoustic transducers. Although it cannot be completely eliminated, suitable steps can be taken to minimise it. However, the user is not interested in why this distortion takes place but in how great the level of distortion must be for it to become perceptible. According to the findings of several research projects, a total harmonic distortion of 1% in the frequency range of 100 to 2000 Hz is imperceptible. Below 100 Hz, the perceptibility threshold lies at 10%. |
| Transducer principle |
| Two transducer principles have become established for the conversion of electric energy into mechanical energy: electrodynamic and electrostatic transducers, whereby the latter is only to be found in audiophile systems, due to their relatively high manufacturing costs. Electrodynamic transducers basically consist of a ring-shaped permanent magnet and an oscillation coil, which is fixed to the receiver diaphragm. When an audio-frequency alternating current is passed through the oscillation coil, it is caused to vibrate in accordance with the audio-frequency alternating current, thus causing the diaphragm to vibrate in the same way. |
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